[RFC] Hybrid live image?

["Yong, Jonathan" <jonathan.yong@intel.com>]

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Hi,

Attached patch makes the init script attempt to find an writable image
to use with Overlay/AUFS, and probably does so poorly.

The idea is to eventually allow users to do a "RESET" option in case
they mess up the system. The underlying image can be something read-only
like cramfs or squashfs.

Any comments or suggestions?

[-- Attachment #2: init-live.txt --]
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diff --git a/meta/recipes-core/initrdscripts/files/init-live.sh b/meta/recipes-core/initrdscripts/files/init-live.sh
index 441b41c..35047c8 100644
--- a/meta/recipes-core/initrdscripts/files/init-live.sh
+++ b/meta/recipes-core/initrdscripts/files/init-live.sh
@@ -152,6 +152,25 @@ do
   sleep 1
 done
 
+try_rw_image() {
+    for i in /run/media/$ROOT_DISK/$ISOLINUX/${ROOT_IMAGE}.rw; do
+        if [ -w $i ]; then
+            mount -o rw,loop,noatime,sync $i /rootfs.rw
+            if [ "$?" -ne 0 ]; then
+                break
+            fi
+            touch /rootfs.rw/.rwtest 2>/dev/null
+            if [ "$?" -ne 0 ]; then
+                break
+            fi
+            rm /rootfs.rw/.rwtest
+            return
+        fi
+     done
+     umount /rootfs.rw
+     mount -t tmpfs -o rw,noatime,mode=755 tmpfs /rootfs.rw
+}
+
 # Try to mount the root image read-write and then boot it up.
 # This function distinguishes between a read-only image and a read-write image.
 # In the former case (typically an iso), it tries to make a union mount if possible.
@@ -159,6 +178,7 @@ done
 mount_and_boot() {
     mkdir $ROOT_MOUNT
     mknod /dev/loop0 b 7 0 2>/dev/null
+    mknod /dev/loop1 b 7 1 2>/dev/null
 
     if ! mount -o rw,loop,noatime,nodiratime /run/media/$ROOT_DISK/$ISOLINUX/$ROOT_IMAGE $ROOT_MOUNT ; then
 	fatal "Could not mount rootfs image"
@@ -187,7 +207,7 @@ mount_and_boot() {
 		rm -rf /rootfs.ro /rootfs.rw
 		fatal "Could not move rootfs mount point"
 	    else
-		mount -t tmpfs -o rw,noatime,mode=755 tmpfs /rootfs.rw
+		try_rw_image
 		mkdir -p /rootfs.rw/upperdir /rootfs.rw/work
 		mount -t overlay overlay -o "lowerdir=/rootfs.ro,upperdir=/rootfs.rw/upperdir,workdir=/rootfs.rw/work" $ROOT_MOUNT
 		mkdir -p $ROOT_MOUNT/rootfs.ro $ROOT_MOUNT/rootfs.rw
@@ -201,7 +221,7 @@ mount_and_boot() {
 		rm -rf /rootfs.ro /rootfs.rw
 		fatal "Could not move rootfs mount point"
 	    else
-		mount -t tmpfs -o rw,noatime,mode=755 tmpfs /rootfs.rw
+		try_rw_image
 		mount -t aufs -o "dirs=/rootfs.rw=rw:/rootfs.ro=ro" aufs $ROOT_MOUNT
 		mkdir -p $ROOT_MOUNT/rootfs.ro $ROOT_MOUNT/rootfs.rw
 		mount --move /rootfs.ro $ROOT_MOUNT/rootfs.ro